Tube-mill shell liner



Dec. 31, 1929. F R BARRATT 1,741,604

TUBE MILIL SHELL LINER lPatented Dec. 31, 1929 UNITED STATES PATENT OFFICE TUBE-MILL SHELL LINER Application led January 5, 1925, Serial No. 686, and in South Africa March 11, 1924.

The present invention relates to liners for the shells of tube mills employed for grinding ores and like substances. The invention also resides in the method of grinding ores including a charge composed of large and small bodies which are of different relative weights so that when the charge is agitated the large bodies will be lifted and allowed to fall as a cascade on the small bodies and at the same time constraining the charge so that the large bodies are directed in one direction and the small bodies in an opposite direction to consequently maintain an even distribution of the charge in the tube mill.

The invention is illustrated in the accompanying drawings in which:

Fig. I is an interior view showing part of a tube mill empty.

Fig- II is a cross sectional view illustratinfr the mill in operation.

rig. III is a schematic view showing the mill cut longitudinally in half on A, B Fig. II and opened out on B.

2 is the shell of the mill. 3 indicates an end plate of the mill and 4: is the hollow trunnion through which the mill charge is fed into the mill. 5 (Fig. III) isA a perforated plate through which comminuted material passes to the outlet trunnion 6.

The shell liner 7 is provided on its internal surface with ribs 8 which extend in the vgeneral direction of the length of the mill.

The purpose of the invention is to cause said ribs to distribute the mill charge (indicated generally by 9) in a manner which improves the efficiency of the mill; and more particularly to convey the large and angular pieces 9a of the mill charge from the inlet end of the mill towards the outlet end and to convey the rather smaller and rounded pieces 9b in the opposite direction, so as to keep the different sized constituents of the mill charge more evenly distributed along the mill than is the case at present.

This object is attained by making the ribs 8 helical, with a long pitch, giving rise to a twist similar to the rifling of a gun as will appear from Fig. I.

The twist of the ribs is of the same hand as that of the rotation of the mill, both viewed from the outlet end of the mill, as in Figs. I and II, in which arrow C indicates the direction of rotation.

The effect of this twist, provided the nitch or inclination of the ribs and their cross section are somewhat as shown, is reflected in Figs. II and III. Fig. II shows the mill rotating whereby the mill charge is carried up on the rising side D of the mill and falls over as a cascade which falls onto the pulp indicated by 10 and also impinges on the opposite side of the mill. The larger nieces 9a of the charge tend t-o fall to the bottom of the mass and into contact with the liner in preference to the smaller pieces of the charge. The ribs tend to engage the pieces of the charge with which they are in contact and to carry them up on the rising side of the mill to a greater degree than the pieces of the charge which arefarther within the interior of the charge, and so out of immediate contact with the liner. Of the charge 'pieces which are in contact with them, the ribs tend to lift selectively the larger and more angular fragments 9a, so that the said larger and angular fragments are lifted to a greater extent than the fragments which have become reduced in size and somewhat rounded.

Such lifting however is far from positive and the fragments, while being lifted, slip relatively to the liner in the direction of gravity, indicated by the arrow G in Fig. III. The inclination of the ribs causes this relative motion between the ribs and the frage ments to have a component in the direction of the arrow E, that is towards t-he outlet end of the mill; and as the larger and more angular pieces on the whole react more with the liner than the other constituents of the charge, said larger and angular fragments are selectively propelled towards the outlet end of the mill.

Considering, on the other hand, the mill charge which falls through the pulp onto the liner on the descending side F of the mill, it will be noted that the inclination of the ribs at the point of the impact is, relatively to gravity, opposite the inclination on the rising side. The falling fragments accordingly tend to glance oil the ribs in the general direction (indicated by arrow H) of the inlet end of the mill; and so, on the whole, to be transported towards that end of the mill. 'lhe charge which thus falls includes a higher percentage of partially reduced and rounded fragments than does the mill charge in contact with the liner on the rising side of the mill, so that there is a tendency for such partially reduced and rounded fragments to be selectively transported towards the inlet end of the mill.

lt is well known that in a tube mill charge a preponderance of large and angular fragments is likely to ,be found at the inlet end of the mill and a preponderance of partially broken and rounded fragments towards the outlet end, with the result that comminution of :the -ore proceeds more actively at the inlet end than towards the outlet end. The effect of selectively transporting the larger and angular pieces towards the outlet end and of selectively transporting the less angular and somewhat reduced pieces in the opposite direction is to make the constitution of the mill charge more uniform throughout the length .of ythe mill and so increase the grinding capacity of the mill.

The pitch or inclination Aof the ribs is such that whilst performing the transporting functions above described, the ribs also function to a material extent as purely longitudinal ribs. That is to say they operate to Aa material. extent to lift the charge on the rising side D of the mill; and to act as an anvil, substantially transverse to the falling material on the opposite side F of the mill, as mentioned above. rlhey also serve to agitate the charge by passing under and penetrating into the same as the mill rotates.

The inclination of the ribs moreover is such that they ldo not to any substantial extent form a transverse barrier which would i tend to hinder free movement of the charge ameter and twenty-two feet long, with a grinding charge consisting of large pieces of ore, the best results have been attained with an angle of about five degrees.

The cross-sectional shape of the ribs which gives the best results in the way of agitating the charge, whilst having a desirable lifting capacity, is that of a wave form.

The curvature of the wave form may diifer on the opposite faces of the wave to promote the two different functions which said faces are intended to perform. The functions of the rising face ll being to lift, transport longitudinally and agitate the charge, it would as a rule have a somewhat steep rise as appears from Figs. I and Il. The reverse face l2 .on the other hand functions chiefly as an anvil on which the mill charge falls on the descending side of the mill and is thereby itself fractured as well as fracturing smaller pieces between itself vand the liner. This face is consequently less steeply inclined so as to be approximately normal (in cross section) to the direction of the falling charge, as seen in Fig. Il.

The liner is conveniently built up of separate blocks as appears from Fig. I. A block comprises a base 13 of voussoir form shaped to fit the mill so that the blocks build up into an arch formation. The base is rectangular in plan, `and the section of the vrib.I which rises from the base is disposed thereto at the desired angle of the rifling and so that las the blocks are placed together in the intended formation, which usually involves breaking joint, the sections of rib aline to form a complete rib extending along the mill.

I claim l. The method of grinding ores including a charge composed of large and small bodies of "a weight less than the large bodies, agitating the charge -to lift the large bodies so that they fall as a cascade on the small bodies, and simultaneously constraining the charge so that the large bodies of the charge are directed in one direction and the small bodies in .an vopposite direction to consequently maintain an even distribution of the bodies of the charge.

2. Ln combination, a tube mill including a cylindrical shell, end plates, inlet and outlet trunnions connected with the respective end plates, a grinding charge comprising large bodies `approximating to spherical form and smaller pebbles of less weight than the large grinding bodies, a liner for the interior of the shell having a plurality of substantially longitudinal ribs extending from one end of the shell to the other and disposed as a heliX of longpitch and of the same hand as the direction of rotation of the shell viewed from the outlet end thereof for agitating the charge during rotation to lift the -large bodies so that they fall as a cascade `on thesmall pebbles and simultaneously constrain the charge so that the large bodies are directed in one direction and the small pebbles in the opposite direction to consequently maintain an equal distribution of the charge, and the inclination of the upper face of the crosssectionbf eachvrib on the rising side of the mill being greater than that of the opposite face, substantially as and for thel purposes set forth.

In testimony whereof I have hereunto set In hand.

FREDERICK REEVES BARRATT. 

